Generally, the focus accommodation of the human eyes (hereinafter simply referred to as “accommodation”) is realized by changing the thickness of the lens. As illustrated in FIG. 18, a lens L is a convex transparent member having a diameter of approximately 9 to 10 mm and a thickness of approximately 4 to 5 mm and exerting a lens function, and is fixed to a ciliary body C by Zinn's zonules Z in such a manner as to be arranged on the rear side of the iris I in a state of being encapsulated by a lens capsule S.
A detailed accommodation mechanism will be described. For example, when a person looks at a distant object, as illustrated in FIG. 18(a), the ciliary muscles Cm of the ciliary bodies C are relaxed and the ciliary bodies C are at positions retracted in a direction away from the lens capsule S. In this state, relatively strong tension is generated in the Zinn's zonules Z positioned between the ciliary bodies C and the lens equators Se. As a result, the lens equators Se are pulled in a radially outward direction to deform the lens L in such away as to decrease the thickness thereof. Accordingly, the thickness of the lens L in the lens capsule S decreases, whereby the focus accommodation during distance vision is realized.
On the other hand, when accommodation is realized to view a near object, as illustrated in FIG. 18(b), the ciliary muscles Cm of the ciliary bodies C are contracted so that the ciliary bodies C protrude centripetally (toward the lens equators Se) and the ciliary bodies C are positioned in a direction closer to the lens capsule S. As a result, since the tension of the Zinn's zonules Z decreases, the thickness of the lens L increases due to the elasticity inherent to the lens, whereby the focus accommodation during near vision is realized. During this focus accommodation, it is known that the closer a portion is located in relation to the center of the anterior capsule Sf, the more the portion is likely to be movable, whereas the posterior capsule Sb is rarely movable.
As described above, the thickness of the lens is changed according to contraction and relaxation of the ciliary muscles of the ciliary bodies to refract light entering the eyes, whereby the focus accommodation is realized. In this accommodation mechanism, it is known that the contraction and relaxation functions of the ciliary muscles of the ciliary bodies are maintained satisfactorily in old ages in the same manner as in young ages. On the other hand, it is also known that, since the contents of the lens and the lens capsule become hardened in old ages and lose flexibility, thus making the thickness of the lens rarely change, the ability (hereinafter referred to as accommodation power) to accommodate the focus range freely from distance vision to near vision is lost (this is referred to as presbyopia).
By the way, a disease called a cataract which is a clouding of the lens mainly resulting from aging is one of the diseases occurring in the lens, and many patients have cataract surgery to treat their cataracts. This surgery generally uses a method in which the anterior capsule is incised in a circular form to create a circular hole, the contents of the cloudy lens are extracted from the hole according to phacoemulsification, and an intraocular lens is inserted into a transparent lens capsule while leaving only the lens capsule with the circular hole formed therein. The cataract surgery based on this method has been currently applied to more than one million patients in Japan every year and more than 3 million patients in the United States of America every year, and the intraocular lenses used for this surgery are generally monofocal lenses.
However, since the monofocal lenses are generally formed of a material such as polymethylmethacrylate (PMMA), silicon, or acryl, and it is not possible to change the thickness of the monofocal lens itself, the loss of the accommodation power after the surgery is unavoidable. In contrast, multifocal lenses which are arranged in a refractive multifocal lens having portions having different refractive powers formed concentrically in an optical portion and a diffractive multifocal lens having a structure causing an optical diffraction phenomenon formed in an optical portion so as to disperse and capture light entering into the eyes are arranged as multifocal lenses for distance vision and near vision (in some cases, for intermediate vision). However, these multifocal intraocular lenses have not reached a sufficient point of satisfaction to meet the demands of patients because there are reports that some patients experience halos where a ring of light appears around an object, trouble such as glare with bright light, a decrease in vision, and insufficient contrast sensitivity.
Moreover, in recent years, as an intraocular lens capable of exerting an accommodation function by a method different from the above-mentioned method, an accommodating intraocular lens including an optical portion formed of a convex lens and two joint-type connection arms arranged in such a manner as to come into contact with the inner side of a lens equator so that accommodation is realized by the optical portion moving back and forth is known (see Patent Document 1 below). In this accommodating intraocular lens, the connection arm is attached to the optical portion at a first position on the connection arm and works harmoniously with the movement of the equator of the lens capsule to which the contraction and relaxation of the ciliary muscles of the ciliary bodies are transmitted via the Zinn's zonules at a second position on the connection arm.
On the other hand, a number of ring-shaped lens capsule expanding devices which are used for expanding the lens capsule before inserting an intraocular lens during cataract surgery have been proposed. These ring-shaped lens capsule expanding devices come in two types depending on the purpose.
One example is called a capsular tension ring (a lens capsule expansion ring) which is an open ring formed in a C-shape. This ring is inserted from the inner side into the lens equators in which the Zinn's zonules are weak and ruptured to expand the lens equators outward to create a round shape.
The other example is called an equator ring which is formed in an O-shape. This ring is a relatively thick closed ring (continuous ring) of which the cross-section has sharp edges such as a square. This ring is arranged on an inner side of the lens equators to form a strong bent portion in the lens capsule to prevent the growth and entrance of lens epithelial cells.